A motor vehicle driver typically controls the speed of a conventional vehicle using foot pedals, which in a vehicle with an automatic transmission are the accelerator pedal and the brake pedal. Drivers will normally use the same foot to control both the accelerator pedal and the brake pedal. However, some drivers of automatic transmission vehicles use two feet, one to actuate the accelerator pedal and the other to actuate the brake pedal. This can result in simultaneous activation of both the vehicle brake and throttle. In certain situations a stall condition may occur due to simultaneous activation of both the brake and the throttle, subjecting the vehicle's drivetrain to significant stress.
Others have attempted to limit drivetrain stress due to simultaneous actuation of the vehicle's brake and accelerator pedals by reducing or limiting the throttle setting under such conditions, thereby limiting the amount of torque generated by the vehicle's engine and delivered to a transmission system. An example may be found in U.S. Pat. No. 6,125,315, issued to Kon, the contents of which are hereby incorporated herein by reference. The system disclosed by Kon limits the degree of opening of the throttle when a stall condition is detected, thereby reducing stress imposed on the vehicle's drivetrain. However, such systems do not address the unique stresses imposed upon a four-wheel drivetrain when a vehicle is operated such that the brake and accelerator pedals are actuated under road conditions wherein some, but not all, of the wheels lose traction.
For example, many vehicles are now equipped with an “on-demand” four-wheel drive transmission system wherein a varying amount of torque is provided to each axle in order to maintain traction under varying road conditions. One of the most severe of these road conditions occurs when the wheels of one axle of the vehicle lose traction due to, for example, ice or snow while the wheels of the other axle retain traction. When launching the vehicle from a stalled state under these conditions a large amount of torque is transferred to the axle having traction due to the lack of traction in the other axle, thereby imposing significant stress upon the drivetrain. However, if a vehicle under the same conditions is equipped with a vehicle stability control system the amount of torque transferred to the axle having traction may be reduced because the vehicle stability system limits and compensates for a loss of traction in the other axle by reducing engine power and applying brake intervention to reduce wheel slip on low traction surfaces. This reduction of wheel slip reduces the amount of torque transferred to the axle having traction, thereby reducing stress on the drivetrain.
It would be desirable to utilize a vehicle's traction control system in conjunction with a throttle limiting system in order to tailor the operating performance of the vehicle under stall launch conditions wherein the brake and throttle are activated simultaneously. Such a system would be particularly useful for increasing the operating performance of an on-demand four-wheel drive transmission under varying road conditions while still protecting the drivetrain from damage.